As depicted in FIG. 5, a chain saw 1 representing one example of the portable working machine is designed such that a guide bar 11 and a saw chain 12 slidably hanged around the guide bar 11 are disposed, as a working member, on the right side of the fore portion of main housing 2. The saw chain 12 is designed to be driven by an internal combustion engine (such as an small air-cooled two-stroke gasoline engine) which is disposed inside the main housing 2.
A rear-handle 14 including a throttle trigger 15 and is attached to a rear portion of the main housing 2. A front-handle 17 having a nearly C-shaped or loop-like configuration is attached to an outer periphery of a central portion of the main housing 2 in such a manner that the front-handle 17 is extended from the left side of the main housing 2. Further, a hand guard 19 is attached to an upper fore-portion of the main housing 2.
On the left side of the main housing 2, there are a cooling fan for cooling the internal combustion engine and a recoil starter (only a starter handle 18 is shown in FIG. 5). An outer casing (fan casing) 20 with a large number of air inlet slits 22 is attached to the left side of the main housing 2 so as to cover the cooling fan as well as the starter.
This chain saw 1 constructed as described above is suitable for cutting and pruning trees and branches. However, as shown in U.S. Pat. No. 5,687,689, this chain saw 1 may also be used in the pruning work of a palm tree.
However, the following problems can occur if the chain saw 1 constructed as described above is to be employed in the pruning work of a palm tree. Namely, not only powdery sawdust but also fibrous sawdust such as cloth scrap-like or waste thread-like sawdust is generated in the pruning work of a palm tree. As a result, this fibrous sawdust gets sucked into the main housing 2 through the air inlet slits 22 of the outer casing 20, thereby clogging the space between the cylinder cover and the cooling fan. As a result of this clogging, the flow of the cooling air is obstructed which greatly deteriorates the performance of cooling fan (air volume) to cool the engine. In order to remove the fibrous sawdust trapped in the space between the cylinder cover and the cooling fan, the outer casing, cylinder cover, and other parts must generally be removed.
With a view to overcome these problems, U.S. Pat. No. 5,687,689 proposes the employment of a mesh member which is designed to be attached to the outer casing so as to cover the air inlet slits thereof.
The idea to directly attach a mesh member to the surface of the outer casing as described in the aforementioned U.S. Patent, however, still has the following problems: (1) the mesh member can be clogged with fibrous sawdust that has been trapped by the mesh member, thereby making it difficult to secure a sufficient performance (air volume) to cool the engine; (2) due to external factors such as the collision of the mesh member with branches of tree, the mesh member may be easily torn or damaged; and (3) it takes time in mounting or exchanging the mesh member.
The present invention is intended to overcome the aforementioned drawbacks, and therefore an object of the present invention is to provide a refuse-trapping cover for a portable working machine, which is capable of reducing the deterioration of the engine-cooling performance of the cooling fan that may be caused by the fibrous sawdust of a palm tree.